Process of dewaxing hydrocarbon oils



Filed Dec. 2, 1938 Dec. 16, 1941.

Patented 'Dec.'16 1941 UNITED 'STATE S PATIENT OFFICE PROCESS F DEWIGHYDEOCABBO Leo D. Jones. Philadelphia. Pa., asslgnor to The SharplesCorporation, Philadelphia, Pa., a corporation of Delaware ApplicationDecember z, 193s.' serial N5. 243,559

(ci. isc- 19) 3Claims.

' centric layers and discharging the materials of these layersseparately from the influence of centrifugal force. It is concernedprimarily with a process of effecting such separation and separatedischarge, but includes as an additional feature a machine havingparticular utility for performing the steps constituting the process ofthe invention. While both the process and machine of the invention willprobably be found useful in the solution of various separation problems,the invention was conceived as a solution of problems arising incidentto the separation of wax from petroleum stock, and has been found to beparticularly useful in connection with these particularproblems. In thefollowingv description, the invention will therefore be discussed in itsrelationship to separation of wax from oil, it being understood thatthis method of description is adopted merely for the purposes ofconvenience of illustration, and not with any intent to limit its scopeto this single use.

The invention may be considered as an improvement over the process ofdewaxing petroleum stocks described in the patent to P. T. Sharples No.1,351,265 of August 3l, 1920. That process has gone into extensivecommercial use in the United States and foreign countries. In

i the practice of the process of that patent, the

stock to be dewaxed is first diluted with a sufficient amount ofrelatively low-boiling hydrocarbon solvent to render the oil phase, uponsubsequent chilling to precipitate wax, distinctly lighter than theprecipitated wax. The diluted stock, containing both oil and wax, isthereafter chilled to a temperature below 0 F. in order to precipitatethe wax from solution in the diluent. The oil solution containing theprecipitated wax is thereafter centrifuged to eect stratification of thewax and separate discharge of the wax and diluted oil phases from thecentrifugal rotor.

In the practice of a process of this charactern attempts have heretoforebeen made to employ centrifugal rotors of the familiar type having aso-called disc-block; i. e., a series of nested, closely spacedfrusto-conical discs affording a plurality of superimposed stratifyingchambers from which the wax passes outwardly beyond the outercircumference of the disc-block and the'oil passes inwardly beyond theinner circumference, the wax and oil being discharged over' separateweirs or ring-dams which control the desired balance of the materialdischarged from Y the wax outlet against the constituents in the mainbody of the centrifugal rotor. In the separation of substances from eachother in separators of this type, the mixture which is subjected tocentrifugation is commonly fed to an intermediate zone of the rotorbetween the outer and inner circumferences of the discs and is passedlongitudinally of the rotor through openings in the discs at that zoneto points between the discs within which stratification occurs. Inattempted separation of wax from diluted petroleum stock by such aprocess, difficulty is frequently encountered because of the fact thatthe wax clogs the spaces between successive stratifying discs and thusrenders continuous centrifugation over a substantial period of timedifficult or impossible. An object of the present invention has been tosolve this problem.

In the process described in the patent to P, T. Sharples No. 1,351,265,a carrier liquid which is immiscible with the oil and wax is employed tofacilitate flow of the wax phase through the centrifugal rotor anddischarge of wax from the rotor. This carrier liquid fulfills theimportant functions of preventing stickage of Wax to parts of the rotor.It also facilitates ow of the wax circumferentially of the rotor to thepoints from which it is discharged from the rotor. An improvementinvented by the present applicant was later used in the practice of theprocess of Patent No. 1,351,265, and this improvement is described andclaimed in the patent to Jones No. 1,649,117. It consists in the feed ofthe carrier liquid to the centrifugal rotor adjacent the point ofdischarge of wax therefrom. An important advantage of this improvementconsists in the fact that it enables the operator to employ carrierliquid in a heated condition, thereby melting the wax and preventingstickage thereof in the apparatus into which it is discharged from therotor. If an attempt were made to feed hot carrier liquid together withthe oil into the centrifugal rotor, this carrier liquid would remeltmuch of the wax precipitated by the preceding chilling loperation andthereby cause resolution of this wax in the oil phase, resulting indischarge of this dissolved wax with the `oil and consequent inadequatedewaxing. By feedingthe carrier liquid at the point of wax discharge, itis possible to employ hot carrier liquid. since the hot carrier liquiddoes not in this case come into contact with the wax until the wax hasbeen separated from the oil layer by stratiiication.

Wax discharged from the centrifugal separator in any centrifugaldewaxing operation contains a substantial quantity of entrained oil, theoil content of the wax varying between and 50%. It is, of course,desirable to reclaim this entrained oil in case this can be doneeconomically. A particular object of the present invention has beentoaord a process whereby the oil entrained in the wax can be economicallyrecovered. f

When a hot carrier liquid is fed to the wax discharge point of acentrifugal rotor provided with a disc-bloc, diiiiculty is encounteredby reason of the fact that the hot carrier liquid transmits heat throughthe thin dividing wall between the wax discharge outlet and the mainbody of the rotor. This transmission of heat results in re-meltng of waxwhich is between the individual discs nearest to the point of waxdischarge with the consequence that this wax is re-dissolved in the oiland discharged with the oil. Another feature of the invention consistsin the development of a machine and process for avoiding this defect.

A still further object of the invention consists in the development of aprocess in which the wax stratified from the oil in the main body of therotor is supported on an auxiliary spacing liquid which lies adjacent tothe inner circumference of the rotor wall and prevents adhesion of waxto that wall, but in which that spacing liquid is not discharged withthe wax and does not therefore contaminate the discharged wax.

In cases in which hot carrier liquid is discharged with the wax, thecarrier liquid must be separated from the wax by somewhat elaborateprocedure before an attempt is made to treat the wax to separate furtheroil therefrom. This procedure involves separating the bulk of thecarrier liquid by gravity settling and partial distillation to evaporatethe last traces of carrier liquid. In case a procedure of this type isadopted, the wax must also be diluted and re-chilled to reprecipitatethe wax prior to the second step of centrifugation. A particular featureof the present invention consists in the performance of the dewaxingoperation in such a way as to avoid pollution of the separated wax withcarrier liquid, and to discharge the wax in dilution in a liquid whichcan be advantageously used in the second step of centrifugation employedto remove entrained oil from the wax. A further feature of the inventionconsists in the discharge of wax in such dilution in a chilled state,thereby avoiding expensive additional chilling to re-precipitate the waxprior to the second centrifuging step.

Further objects and advantages of the invention will be evident from areading of the following specification in the light of the attacheddrawing, in which the single figure is a crosssectional view of acentrifugal separator embodying the mechanical features of the inventionand in which the process features of the invention may be practiced.

Referring to the drawing by reference characters, the rotor I8 of thecentrifugal separator is driven by suitable. means such as the shaft 28illustrated in the drawing. 'I'hs rotor comprises a main body portion Iland-a top portion I2 secured to the main body portion in conventionalmanner by a clamping ring I3. A disc-bloc I4, consisting of a pluralityof nested frusto-conical stratifying discs, is secured in positionwithin the rotor between the top portion I2 and the main body portionII. The construction of these discs constitutes an important feature ofthe invention,

` as will be discussed hereinafter. A tube I5 may be secured to theinterior of the rotor and receives from the feed conduit I 6 thematerial to be treated. The tube I5 communicates with the main body ofthe rotor through a plurality of openings 29 adjacent the base of therotor, these openings directing the mixture under treatment into thespace 26 surrounding the outer circumference 25 of the disc-bloc. Therotor is provided with a plurality of discharge outlets I1 communicatingwith the 'outer portion of the separating space 26 and adapted toreceive the heavy eiiiuent from the rotor after that effluent has passedaround the outer circumference of the frusto-conical disc I8 whichconstitutes the dividing wall for separating and separately dischargingthe light and heavy eiliuents respectively. Material passing upwardlythrough outlet I1 passes around ring-dam I9 into a cover 20 ofconventional design. The light eiiiuent from the rotor passes inwardlybetween the respective discs of the disc-bloc I4 and is dischargedthrough space 2I communicating with the inner circumference of thedisc-bloc, into the light eiiiuent receiving cover 22.

A conduit 23 is provided between the covers 28 and 22 and conveys liquidto a nozzle 24 similar to that described in the patent to Jones No.1,649,117, and this liquid is thereafter directed into the centrifugalrotor adjacent the point of discharge of light eiliuent'from the rotorover ring-dam I8, just as in the case of applicants prior Patent1,649,117.

The bottom of the upper cover 22 is separated from the top of the lowercover 28 by an insulating air space, thereby preventing undesiredchilling of wax discharged into cover 20 by oil discharged into cover22. Y

A feature of the invention consists in the provision of a dividing WallI8, which is in laminated form and provided with insulation 21 betweenits upper and lower surfaces.

The advantages of the above described centrifugal separator and thenature of the process of the present invention will be obvious from thefollowing description of that process in the illustrative embodimentsdiscussed hereinafter.

In the practice of the process of the invention using the machinedescribed above, a mixture containing oil diluted with naphtha, hexane,or other diluent of sufficiently low specific gravity and in sufficientquantity to render the oil phase substantially lighter than theprecipitated wax phase, and containing precipitated wax, is fed throughconduit I6 into the feed tube I5 of the rotor. This mixture passesoutwardly through openings 28 into the stratifying space 26. Inaccordance with the invention, this space 25 is relatively large,thediscs of disc-bloc I4 being relatively small in diameter, andterminating a considerable distance radially within the zone occupied bythe plastic wax layer which separates from the oil solution. It willthus be seen that the principal stratifying action of the rotor occursin the space 26, which lies entirely outwardly of the disc-bloc. Oilpassing inwardly into the disc-bloc has therefore been deprived of themajor part of its wax, and the wax content of such oil consists entirelyof small quantities of finely divided wax which have not been removedincident to the stratifying action which takes place in the outercircumferential zone 26. By reason of this fact, the cloggage of discsby wax,

assauts such as heretofore occurred inthe attempted use of a disc-blocin centrifugal dewaxing is avoided. The disc-bloc is used only toseparate the last traces of wax from oil and deliver into the space 2land cover 22 a thoroughly dewaxed oil. Since only small quantities ofwax pass outwardly from the disc-bloc into the space 26, cloggage isavoided.

The wax which separates as an outer stratum in the outer part of thespace 28 passes upwardly around the outer edge of the dividing wall I8and is discharged through passages I1 and around ring-dam I9 into thecover 20, this wax being balanced against the concentric strata of waxand oil in the main body of the rotor.

A carrier liquid, such as hot water or brine, may be introduced throughthe conduit 23 and nozzle 24 into the upper part of the passages I1adjacent the ring-dam I9. In case such carrier liquid is used, a part ofthis carrier liquid will pass downwardly through the passages I1 intothe main body of the rotor. If a hot carrier liquid were used in thismanner in a machine of conventional design employing a disc-bloc, thehot carrier liquid would transmit heat through the dividing Wall andcause melting of Wax within the upper section of the disc-bloc. Thiswould result in re-solution of that wax in the oil and discharge thereofwith the oil, thereby impairing the efliciency of the centrifugaldewaxing operation. In accordance with the present invention, thisundesired re-melting of wax is avoided by providing an insulating strip2l, which eii'ectively prevents the undesired conduction of heat to themixture of oil and wax adjacent the dividing wall I Q8.

In the preferred embodiment of the invention, no carrier liquid is used,since it is desirable that wax be free of contamination with carrierliquid in order that it may be promptly subjected to further processingin a chilled condition to remove residual oil and thus reclaim that oil.This result is accomplished by feeding through the conduit 23 and nozzle24 a diluent for the wax which is miscible with the oil and of lowerspecific gravity than the wax itself. This diluent may be a lighthydrocarbon such as hexane or naphtha, or it may be any liquid capableof softening the wax and preventing adhesion thereof to the parts of thecover 2U. By adding this diluent in a sufiicient proportion to effectthe desired softening and avoid stickage at these points, it has beenfound possible to'perform the dewaxing operation without the use of anaqueous carrier liquid and consequent discharge of the carrier liquidwith the wax.

A further feature of the invention consists in the provision of anauxiliary spacing liquid which prevents adhesion of wax to the innercircumferential wall of the rotor and facilitates flow of waxcircumferentially around the rotor to the discharge points, but is notdischarged with the wax. Thus, a liquid such as water or brine may beintroduced into the centrifugal rotor in sufficient quantity to form athin spacing layer of liquid within the wall of the centrifugal rotor.This layer prevents adhesion of wax to the rotor wall, but it issuiciently thin so that it does not extend inwardly as far as the outercircumference of the dividing wall IB, and does not therefore preventcontinuous discharge of wax from the rotor. This feature -of the use ofa layer of spacing liquid may be advantageously used in conjunction withthe feed of a non-aqueous softening liquid to the upper end of the rotorto assist in discharge of wax over the ring-dam I9.

The injection of a hydrocarbon diluent adjacent the zone of discharge ofwax over ringdam Il has an additional advantage in connec-J tion .withfurther processing of the wax by centrifugation or otherwise to removeentrained oil. In prior art practice in which a hot carrier liquid wasemployed, the use of such liquid introduced two factors of expense intoany processv designed to recover entrained oil from the wax. In thefirst place, the carrier liquid. being hot, heated the wax, and the waxtherefore required further chilling to precipitate it before beingre-centrifuged. In the second place, the carrier liquid had to beremoved before such re-chilling and re-running, thereby causing expenseincident to this removal step.v

When a softening liquid such asnaphtha or hexane, which is miscible withthe oil entrained in the wax, is introduced through the nozzle 24, allof these items of expense are avoided. In the first place, thehydrocarbon or other liquid added through the nozzle 24 may be atapproximately the same temperature as the wax, and it does not thereforemelt the wax. In the second place, this liquid acts as a very desirablediluent in the performance of the ensuing operation of centrifugation toremove further oil and diluent from the wax. The addition of a diluentprior to the recentrifuging of the wax is desirable in any case. and theamount of diluent which is added through the nozzle 24 is usuallyconsiderably less than the amount of such diluent actually required inorder to re-centrifuge the mixture of oil and wax discharging over thering-dam I9. In view of the fact that the mixture discharged from thecover 20 is already at approximately the same temperature as that of themixture introduced into the feed tube i5, the wax is in a precipitatedcondition in the hydrocarbon diluent-oil solution discharged from cover20, and this mixture therefore requires no further chilling, or at leastonly slight further chilling 'prior to the second step of centrifugationby which further oil is recovered from the wax.

In a typical example of the practice of the present invention, ahydrocarbon stock containing wax was mixed with three times its volumeof naphtha,. The solution so produced Was chilled tated wax was then fedto the centrifugal separator of the invention at a rate of ten gallonsper minute, and a spacing layer of brine was fed to the centrifugalrotor before this feed of petroleum stock thereto was commenced, thisbrine occupying a thin annular space about the inner circumference ofthe rotor section I i, but not extending inwardly as far as the outercircumference of the dividing wall i8. The mixture of oii and wax waspassed into the separating space 2@ of the rotor and the wax wasstratified from the oil, forming a plastic wax layer occupying a zoneextending inwardly from the inner circumference of the layer of spacingliquid to a point about midway radially between the outer circumferenceof the dividing wall I8 and the outer circumference of the disc-blocIrl. The oil passing inwardly into the disc-bloc I4 contained onlyresidual traces of wax. Such wax was removed from the oil centrifugallyin the disc-bloc and impelled outwardly under the iniluence ofcentrifugal force into the Wax stratum occupying the outer portion ofthe stratifying space 26. A thoroughly dewaxed oil was dischargedinwardly through the space 2l into cover 22. Wax from the plastic waxlayer was discharged continuously around the outer circumference of thedividing wall I8 and through the passages Il over ring-dam I9. Naphthawas fed through nozzle 24 to this plastic wax eiiiuent at a point justWithin the rotor adjacent ring-dam I9. The rate of discharge from theplastic wax stratum aroundv ring-dam i9 was 1.5 gallons per minute. Therate of feed of naphtha from nozzle 24 was 1.2 gallons per minute. Thewax diluted with naphtha from nozzle 24 was discharged from the cover 20and was thereafter mixed with an equal volume of naphtha, which had beenpreviously chilledl to the dewaxing temperature. The mixture so producedwas thereafter passed to a secondcentrifugal separator to eilect furtherremoval of oil solution from the wax.

Modifications will be obvious to those skilled in the art, and I do nottherefore wish to be limited except by the scope of the sub-joinedclaims.

I claim:

1. Method of centrifugally classifying components of a mixtureconsisting of a solid having a higher specific gravity characteristicthan a liquid admixed therewith that comprises introducing the mixtureinitially into an external substantially unobstructed annular rst zoneof a centrifugal rotor having a volume at least sumcient to accommodatethe entire separated heavier components; stratifying the mixture whilein said rst zone; passing the lighter components to an internal secondzone immediately contiguous said first zone wherein stratification discsassist further separation of the components; withdrawing the separatedlighter components from a locality near the center of the second zone;withdrawing the separated heavier components from near theouterperiphery of the rst zone in the presence of a hot carrier liquid,immiscible with said heavier components, and having a higher specificgravity than the heavier components, introduced into said heaviercomponents near the place of discharge thereof.

2.. The process of separating into its constituents a mixture of liquidand solids of higher specic gravity than said liquid, which comprisespassing said mixture directly to a zone of a centrifugal rotor free ofstratifying discs, centrifugally stratifying solids from liquid in saidzone of said rotor free of stratifying discs to form a stratum of solidslying entirely-within said unobstructed zone, passing the liquid fromwhich solids have been removed by said rst-mentioned stratifying actioninwardly to a disc-bloc zone of said rotor occupied by nestedstratifying discs, subjecting said liquid to further centrifugationwithin said disc-bloc zone to remove residual solids therefrom,separately discharging liquid, and solids from said stratum of solids,under liquid balance from said centrifugal rotor, passing a hot carrierliquid which is immiscible with the solids and is of higher specicgravity than said solids to the centrifugal rotor and into said solidsstratum adjacent the zone of discharge of 'solids from the centrifugalrotor and insulating the disc-bloc zone of said rotor from the zone ofsaid rotor at' which the carrier liquid enters the rotor.

3. The process of dewaxing a mixture which consists o! precipitated waxin an oil solution consisting of oil and solvent of such character, andpresent in such amount, as to make said oil solution of lower specificgravity than said wax, which comprises passing said solution directly toa zone of a centrifugal rotor free of stratifying discs, centrifugallystratifying Wax from said oil solution in said zone of said rotor freeof stratitying discs to form a plastic wax stratum lying entirely withinsaid unobstructed zone, passing the oil solution from which wax has beenremoved by said first-mentioned stratifying action inwardly to adisc-bloc zone of said rotor, subjecting said oil solution to furthercentrifugation within said disc-bloc zone to remove residual waxtherefrom, separately discharging oil solution, and wax from saidplastic wax stratum, under liquid balance from said centrifugal rotor,passing a hot carrier liquid which is immiscible with the wax and is ofhigher specic gravity than said plastic wax stratum' to the centrifugalrotor and into said wax stratum adjacent the zone of discharge of waxfrom the centrifugal rotor and insulating the disc-bloc zone of saidrotor from the zone of said rotor at which the carrier liquid enters therotor.

LEO D. JONES.

